You've provided no indication of your level of Perl expertise or the context of the project you're working on. Accordingly, I'll assume the lowest common denominators for both: minimal Perl knowledge and a small (personal/hobby/learning) project.

Read "perlintro: Perl introduction for beginners". Each section is fairly basic but also provides links to more detailed information and advanced topics: follow these as required.

For "I have to read this file", you'll want to focus on the "Files and I/O" section in that document.

For your database work, look at DBI. This isn't a core (builtin) module so you'll need to install it: you can use the builtin cpan utility for that task.

You'll also need a database driver module (and you'll need to install that as well). These modules have names like DBD::xxx, where xxx will be something like Oracle. You provided no information about the database system you're using; search CPAN for an appropriate "DBD:: module".

At some later point, having done all this, you may require further assistance. To get the best and quickest responses, follow the guidelines in "How do I post a question effectively?".